Apparatus for measuring variations in thickness of metallic bodies



July 21, 1931. H. E. KRANZ l DIES APPARATUS FOR MEASURING vARIATIoNs INTHIcKNEss oFv METALLIC Bo Filed Jan. l2, 1926 IIII .alma/asa July21.1931@ UNITED STATES PATENT OFFICE HERMANN ERNEST kIKIRANZ, OFIBERWYN, ILLINOINS, ASSGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED,F. NEW YORK, 'N'. Y., A CORPORATION 0F NEW YORK APPARATUS FOR IEASURINGVARIATIONS IN THICKNESS OF METALLIC BODIES 'This invention relates to`apparatus for measuring variations in thickness of m'etallic bodies, anobject being to provide an apparatusof the above character for measuringy metallic bodies such as sheeting, tubes and the like, in which it isdiiicult, if not practiically impossible, to measure the variations inthickness by mechanical instruments.v In accordance with one embodiment,the lo invention contemplates the use of an oscillating circuit of anelectron discharge device having a coil connection adapted to be ap-,pplied in close proximity to the surface of the metallic body, thethickness of which is to '15'be measured and in which the oscillatorcircuit is affected by variations in thickness of the metallic body, sothat an indicating de- Q vice or a meter in circuit therewith will showthe variations in thickness.

For a better understanding of the invention to the accompanyingreference is to be had drawings, in which Fig. 1 is a diagrammatic viewillustrating f thepreferred circuit arrangement of this invention; and

Fig. 2 shows dagrammatically, the apparatus applied to the leadsheathing .of an electric cable for measuring variations in thicknessthereof during its manufacture.

Referring now to the circuit arrangement of Fig. 1, there is providedvasuitable oscillating circuit and preferably of the electron dischargetype in which a tuned grid oscillator circuit is used. A three elementtube 5 is provided having its filament connected with a batteryk 6through a suitable rheostat 7 and ammeter AM. The filament and gridelements of the tube 5 are connected to provide an oscillation circuitin the closed in-' ductance capacity path including the condenser 8,variometer 13 and coil 14, a battery `9 being provided and connectedacross a coni denser 10 through a potentiometer 11 to which a voltmeterV `is connected for measuring the voltage supplied. Th'e plate electrodeof the tube 5 is connected through the battery 12 to the inductance coilor variometer 13 with a suitable voltmeter V con-Y nected across thebattery terminals.

For measuring purposes a measuring coil Application med January 12,1926. Serial No. 80,88.

14 has a support 15 shaped so that it may be placed in close proximityto the surface of the metallicbody which is to be measured is provided.This coil is suitably connected to the oscillator circuit so as to beaffected thereby,'and it is preferably connected in the circuit so thatthe oscillating current will flow therethrough.

The shape of this coil and its support depends upon the use to which thecoil is to be put. If a Hat body or sheet is to be measured, a flatsupport is provided, and if it is to be used on tubular sheathing suchas is placed around an electrical conducting cable for protectivepurposes, a support 15 such as is shown in Fig. 2 may be provided sothat it will ride upon the surface of the tube.

Referring now to the operation of the apparatus, it is first properlyadjusted so as to secure a sustained oscillation, the circuit shownbeing one in which the oscillatory current Hows in the resonant circuitconsisting of the'inductance or variometer 13, the coil 14 and thecapacity 8. -The measuring coil 14 is included in this circuit so thatthe oscillation current flows therethrough.

Any movement of the coil 14 overthey sheathing of varying thickness willcause a change in the amplitude of the oscillating current. This changein the amplitude of the oscillation current is reflected in the platecircuit of the electron tube 5 as a change in the plate current. Thisplate circuit includes a suitable indicating apparatus and ably amilliammeter'MA is connected irectly referin the plate circuit so as toindicate the variationstherein, and which/variations correspond tovariations inthe resonant circuit4 caused by variations in thickness ofthe metallic 'plate'which is being measured. Thus as the coil 14 ismoved over the surface of the metallic plate, variations in thicknessare visually indicated by the milliammeter MA. This milliammeter may bescaled in any suitable way, .such as for indicating the lineardifferences in thickness.

In Fig. 2 the invention is shown appliedy for measuring variations insheathing as it is being applied to electrical cable as it comes fromthe extrusion press. Such a cable that the cable as it leaves the pressis covered withthe lead sheathing.

By applying the measuring apparatus of the present invention -to thecable as it leaves the press and applying coil 14 on the` cable adjacentto the die block where the cable leaves the press, ythe operator canreadily detect any variations in thickness of the sheath and the heatingof the die blocks can be arranged Iso that when any variation appearsthe heat on the die block'can be adjusted accordingly so that a sheathof uniform thickness will be produced.

Although a particular form of apparatus has been shown applied to atubular sheathing it is obvious that other arrangements than that shownand described could be employed without departing from the spirit andscope of the appended claims.

` What is claimed is:

1. In a measuring apparatus, a tuned grid y oscillator circuit having avacuum tube plate,

a grid and filament included therein, means for adjusting said circuitto produce resonance therein, an independently voperable measuring coil:connected with said circuit with the oscillating current lflowing'therethrough,l a support for said measuring coil shaped to be placed. indirect contact with a metallic body, ythe thickness of which is to bemeasured, said oscillator circuit varying responsive to variations inthickness of the body as the coil and thesupport are movedy over thesurface thereof, and means included in a plate circuit of the vacullmtube responsive to such variations in the oscillator circuit forindicating-variations in thickness. p

2. In an apparatus for measuring the thickness of metallic bodiesincluding an electron discharge tube oscillator circuit having a gridand filament included therein, means for adj ustingv said circuit toproduce resonance therein, an independently operable measuring coil incircuit therewith subject to said oscillations, va support for said.measuring coil shaped vto be placed'in direct contact with the metallicbody lwhereby there will be a variation of-,amplitude ofthe oscillatingcurrent according to variations in the thickness of the metallic body, aplate circuit responsive to such variations of the oscillating current,means for negatively biasing the grid, and means connected with theplate circuit responsive to said variations in the plate circuit forvisually indicating the variations in thickcomprising an electrondischarge tube having filament, grid, and plate elements, an oscillatorcircuit consisting of a'detector coil having a support designed to beplaced in direct contact with the metallic bodies, a coil of avariometer for producing resonance, and a condenser in series, a latecircuit including a Second coil of the` a orementibned variometer, agrid circuit connected to the oscillation circuit between the detectorcoil and the condenser, and means connected in the plate circuit forindicating variations in thickness of the metallic bodies.

In witness whereof, I hereunto subscribe my name this 22nd day ofDecember, A. D. 1925.

HERMANN ERNEST KRANZ.

